I look it this in terms of energy expenditures. A car at 25mpg consumes 1250 Kcals/ mile. A motorcycle at 40mpg 775, A Tesla 258 KCals. A bicyclist, 65 KCals/mile. Energy expenditures= extraction of resources= environmental impact. I think putting every form of transportation on the same scale helps highlight the impact or our transportation choices.
Of course the above assumes single occupancy: A car with 4 passengers is 314, a MC w/2 is 387, Tesla 65, and a bike is kind of stuck at 65.
This is something that I have been thinking about. Why do we need 5,000 lb plus vehicles? Well to protect us from other 5,000 lb plus vehicles, right? And as speed in creases the force of impact increases, so we need more protection which usually weighs more, and so on. It is kind of a viscous cycle. At the same time the vast number of car trips are short (under 10 miles) and probably never hit over 30 MPH.) You could design an electric car that would easily go over a hundred miles on a charge if it only weighed 1000 lbs. and didnt go over 30 MPH. What if urban areas turned their roads only into "SOV-lite" vehicles with speed limits of 30 MPH with designated transit roads and (of course) increased in transit offerings? There is in fact a rough equivalent of the vehicle in question: Arcimoto (
https://www.arcimoto.com/) Its KCals/mile is 120, better than a Tesla not quite a bicycle. I think this vehicle or its something like it may be the future of transportation for single occupancy, and with two occupants is 60 KCals/mile or on par with a bicycle.
The other 5000 lbs vehicles that we all fear getting hit buy in our car are either other 5000lb SOVs or delivery vehicles. of some sort. So if we get beyond all having 5000lb 140HP + cars then the remaining issue is delivery vehicles. Now the theoretical 1000lb electric vehicle wouldn't be going on the freeway so no issues with trucks there- the issue would be to either end or manage the co-mingling of delivery vehicles in the "last mile" from getting off controlled access roads to delivery. I do not really have an answer for that. But I do agree that continuing on our present course is not sustainable.,